The reactive adsorption of azo dye from aqueous solutions by powdered activated carbon (PAC) and pumice was investigated. The impacts of several parameters, such as adsorbent quantity, pH, initial dye concentration, and stirring velocity on adsorption, were examined. The pseudo first- and second-order kinetic models were applied to describe the kinetic data, and to evaluate the rate constants. For both adsorbents, i.e. PAC and pumice, the experimental data fitted well with the second-order kinetic model, indicating that chemical sorption was the rate-limiting step of mass transfer.